1. Field of the Invention
This invention relates generally to a valve block, which is joinable to a receptacle to form a container. Containers of such type are suitable for storing liquid, and dispensing a vapor phase from the liquid in a carrier gas passed in contact therewith, and are also useful for containing a sorbent medium to effect purification of an impurity-containing gas flowed through the container.
2. Description of the Related Art
In many industrial applications, it is desirable to transfer a vapor component in a carrier gas medium, the carrier gas generally being inert in the application for which the vapor is present as an active constituent.
An example of such application is in the manufacture of semiconductor devices, in which the vapor constituent may be a dopant, etchant, or conductive material, which is deposited on the semiconductor substrate.
In such semiconductor manufacture applications, numerous vapor constituents are highly toxic in character, particularly those which are source reagents for metallic components such as beryllium, cadmium, selenium, tellurium, and the like.
Accordingly, it has been common practice in the art to employ liquid storage devices for the precursor liquids from which the vapor constituent is derived. In operation, the vapor phase is dispensed by passage of a carrier gas in contact with the liquid in the storage/dispensing device, so that vapor is picked up by the carrier gas and flowed therein to the point of use in the manufacturing system.
Due to the high purities required for the vapor constituent in such applications, it is critical that the carrier gas and vapor constituent be of high purity. Further, there must be no significant contaminants introduced into the carrier gas of the vapor constituent in the contacting step, when the carrier gas is passed in contact with the liquid from which the vapor constituent is derived.
Similarly, due to the purity requirements for semiconductor source reagent gases, it is frequently necessary to purify such reagent gases of contaminants by contacting the gases with sorbent materials selective for the undesired contaminants. The contacting vessels containing the sorbent materials are therefore leak-tightly constructed to avoid atmospheric or environmental contamination of the process gases, as well as to prevent the loss of process gases from the vessel, especially when the same are toxic in character.
One significant problem in the operation of previously-developed liquid storage/vapor dispensing containers and sorbent containers is the fact that they typically have "dead spaces" which are difficult to purge. As a result, hold-up gas trapped in such dead spaces is introduced into the processing system, with consequent adverse effect on the downstream operation to which the process gases are transmitted.
More specifically, the conventional liquid storage/vapor dispensing device is constructed as an assembly of a cup in which the liquid is retained, and a valve block overlying and enclosing the cup. The valve block features an inlet for introducing carrier gas into the cup, and an outlet for discharging carrier gas containing vapor derived from the liquid in the cup. Thus, the inlet and outlet communicate with interior passages in the valve block, which in turn communicate with the interior volume of the cup.
In use, a carrier gas source, e.g., a gas cylinder, is coupled by means of suitable valving and connectors to the inlet. The outlet is similarly coupled by suitable valve and connecting means to flow circuitry for conveying the vapor-containing gas to ultimate end use apparatus.
In such devices, when the respective valves associated with the inlet and outlet are opened, and gas is admitted to the system, the hold-up volume of dead space gas in the valve block is displaced into the outlet conduit and carried to the end use apparatus.
Since the dead space gas is typically air or atmospheric gases, significant contamination of the gas occurs, which may necessitate wasting of the hold-up gas. As indicated, the liquid may yield highly toxic vapor constituents. This in turn may raise a significant disposal problem for the hold-up gas, if it contains any concentration of the vapor constituent.
Alternatively, if the hold-up gas is not wasted, there may be significant contamination of the vapor component by the hold-up gas, which will adversely affect the end use application. For example, in the manufacture of semiconductors, any minute impurity components in the dopant, source reagent, etc., may render the semiconductor device defective or even useless for its intended purpose.
Thus, a major problem associated with the purging of the liquid storage/vapor dispensing device, by passage of inert or carrier gas through the device, is that such gas tends to contact and contain significant quantities of the vapor component derived from the liquid in the device. Where such vapor is highly toxic, as is the case in many semiconductor manufacture applications, it is apparent that the resulting gas mixture produces either an undesirable disposal problem upon purging, due to the toxic constituents of the gas, or else introduces significant impurities to the final product manufactured from the vapor constituent.
Apart from the aforementioned considerations associated with dead spaces in the valve block, the liquid storage/vapor dispensing device is desirably constructed with a minimum of joints, and external welds. Such joints and welds are sources of potential leakage and failure in the device. Furthermore, such joints and welds are not easily inspected while the device is in operation, to determine whether complete structural integrity (leak-tightness) has been maintained.
Similar problems and considerations are applicable to sorbent containers in which a sorbent medium is contained in a receptacle joined to a valve block regulating gas flows through the sorbent bed.
Accordingly, it would be a significant advance in the art to provide a valve block, suitable for application to liquid storage/vapor dispensing containers, or to sorbent containers, which is readily purged of the hold-up gas retained in the "dead spaces" of the inlet, outlet, and associated passages of the valve block.
It therefore is an object of the present invention to provide a valve block for such containers, which is readily purged of "dead space" gas.
It is another object of the invention to provide a container comprising a valve block of such type, which is readily fabricated and simple in construction.
It is a further object of the invention to provide a valve block-equipped container of the aforementioned type, having a minimum number of joints and seals, such as may be latently susceptible in operation to leakage of fluid into or out of the container.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.